Optical Measurements of SuperSpec: A Millimeter-Wave On-Chip Spectrometer

Abstract

SuperSpec is a novel on-chip spectrometer we are developing for (sub)millimeter wavelength astronomy. Our approach utilizes a filterbank of moderate resolution ($R \sim 500{)}$ channels, coupled to lumped element kinetic inductance detectors (KIDs), all integrated onto a single silicon chip. The channels are half-wave resonators formed by lithographically depositing segments of superconducting transmission line, and the KIDs are titanium nitride resonators. Here we present optical measurements of a first generation prototype, operating in the 180–280 GHz frequency range. We have used a coherent source to measure the spectral profiles of 17 channels, which achieve linewidths corresponding to quality factors as high as $Q_\mathrm {filt} = 700{,}$ consistent with the designed values plus additional dissipation characterized by $Q_i \approx 1440{.}$ We have also used a Fourier Transform Spectrometer to characterize the spectral purity of all 72 channels on the chip, and measure typical out of band responses ${\sim }30$ dB below the peak response.